Molecular insights into adhesive mechanisms of phosphate-based dental adhesives on zirconia surfaces: effects of zirconia crystal structure

This paper analyses the adhesion mechanisms of phosphate-based dental adhesives to zirconia materials based on density functional theory (DFT). Zirconia can be a mixture of three crystal structures: monoclinic, tetragonal and cubic. We investigated how these crystal surfaces influence adhesion. On all crystal surfaces, proton transfer occurs from the phosphate group in the adhesive to the zirconia surface. Among the surfaces, the monoclinic surface exhibits the highest adhesive strength. Interfacial interactions involving charge transfer are observed at all adhesive interfaces, which are particularly significant on the monoclinic surface. This is attributed to the low-coordination number of zirconium atoms specific to the monoclinic surface. Moreover, the strong Lewis basicity of these low-coordination zirconium atoms induces structural changes in the methacryloyl group, which acts as polymerization sites in the adhesive. These findings provide valuable insights for guiding the design of zirconia-based dental materials.

The absorption properties of ZrO2 nanoparticles in the THz and sub-THz frequency ranges

As terahertz (THz) and sub-THz region electromagnetic waves are becoming vital for industrial applications such as 5G wireless communication, so too are THz and sub-THz wave absorbing materials. Herein, we report the optical properties of monoclinic zirconia (m-ZrO2) nanoparticles in these frequency regions, with different crystalline sizes. The crystalline sizes of the three samples, measured by transmission electron microscopy, are 93 ± 23 nm (denoted 1), 28 ± 14 nm (denoted 2) and 2.6 ± 0.7 nm (denoted 3). X-ray diffraction and Raman spectra show that 1 and 2 have high crystallinity whereas 3 shows peak broadening due to its small crystalline size. Terahertz time-domain spectroscopy (THz-TDS) measurements of pelletised samples show that the small crystalline size sample exhibits larger absorption, e.g., the absorbance value at 300 GHz is 0.18 mm-1 (1), 0.04 mm-1 (2) and 1.11 mm-1 (3), and the related dielectric loss value (ε'') is 0.04 (1), 0.01 (2) and 0.82 (3), respectively. This is considered to be due to the proportional increase in surface water molecules for the small particle size sample due to the relative increase in surface area and under-coordinated atoms, shown by IR spectra. These results show that small crystalline size m-ZrO2 nanoparticles have potential as THz and sub-THz wave absorbing materials, which are crucial for noise reduction in THz and sub-THz wave technologies.

Unraveling the effect of particle size of active metals in Ni/MgO on methane activation and carbon growth mechanism

For dry reforming of methane, the active metal particle size of the catalyst has a significant effect on both the reaction activity and the resistance to carbon deposition. In this study, nickel particles of different sizes (Ni13, Ni25, and Ni37) supported on the MgO(100) slab are used to study the mechanism of CH4 activation and carbon growth based on DFT theoretical calculations. According to the results, the energy of adsorption for reaction intermediates changes depending on the size of the active metal. The adsorption process of CH3, CH2, CH and C on Ni25/MgO has a maximum exothermic value. Furthermore, the energy barriers of CH4 four-step dehydrogenation are lowest on Ni25/MgO during the CH4 activation process. The growth process of carbon deposition on the catalysts is also investigated in this work. The results indicate that the growth of carbon from C5 to C6 is difficult to proceed on Ni13/MgO due to size and active site limitation. Additionally, with an increase in particle size of the active metal, the absolute value of growth energy and average carbon binding energy of Cn increase on both Ni25/MgO and Ni37/MgO. It is proved that smaller particle size presents better resistance to carbon deposition. In the studied size range, Ni25/MgO is demonstrated to have greater catalytic activity and better resistance to carbon deposition.

Oscillatory Behaviour of Ni Supported on ZrO2 in the Catalytic Partial Oxidation of Methane as Determined by Activation Procedure

Ni/ZrO₂ catalysts, active and selective for the catalytic partial oxidation of methane to syngas (CH₄-CPO), were prepared by the dry impregnation of zirconium oxyhydroxide (Z_hy) or monoclinic ZrO₂ (Z_m), calcination at 1173 K and activation by different procedures: oxidation-reduction (ox-red) or direct reduction (red). The characterization included XRD, FESEM, in situ FTIR and Raman spectroscopies, TPR, and specific surface area measurements. Catalytic activity experiments were carried out in a flow apparatus with a mixture of CH₄:O₂ = 2:1 in a short contact time. Compared to Z_m, Z_hy favoured the formation of smaller NiO particles, implying a higher number of Ni sites strongly interacting with the support. In all the activated Ni/ZrO₂ catalysts, the Ni-ZrO₂ interaction was strong enough to limit Ni aggregation during the catalytic runs. The catalytic activity depended on the activation procedures; the ox-red treatment yielded very active and stable catalysts, whereas the red treatment yielded catalysts with oscillating activity, ascribed to the formation of Ni^δ+ carbide-like species. The results suggested that Ni dispersion was not the main factor affecting the activity, and that active sites for CH₄-CPO could be Ni species at the boundary of the metal particles in a specific configuration and nuclearity.

Structural, electronic, and magnetic properties of Ni nanoparticles supported on the TiC(001) surface

Metals supported on transition metal carbides are known to exhibit good catalytic activity and selectivity, which is interpreted in terms of electron polarization induced by the support. In the present work we go one step further and investigate the effect that a titanium carbide (TiC) support has on the structural, electronic, and magnetic properties of a series of Ni nanoparticles of increasing size exhibiting a two- or three-dimensional morphology. The obtained results show that three-dimensional nanoparticles are more stable and easier to form than their homologous two-dimensional counterparts. Also, comparison to previous results indicates that, when used as the support, transition metal carbides have a marked different chemical activity with respect to oxides. The analysis of the magnetic moments of the supported nanoparticles evidences a considerable quenching of the magnetic moment that affects mainly the Ni atoms in close contact with the TiC substrate indicating that these atoms are likely to be responsible for the catalytic activity reported for these systems. The analysis of the electronic structure reveals the existence of chemical interactions between the Ni nanoparticles and the TiC support, even if the net charge transfer between both systems is negligible.

Ab initio investigation of the formation mechanism of nano-interfaces between 3d-late transition-metals and ZrO2 nanoclusters

Understanding the formation of nano-interfaces between metallic clusters and nanoscale metal-oxides is an important step towards using such systems for catalytic applications. Thus, in this work, we employ density functional theory calculations to study the TMn-(ZrO2)13 interactions, for TM = Fe, Co, Ni, or Cu, and n = 1, 4, and 8. We found a general trend for adsorption and interaction energies (ad/int) for all cluster sizes, with . In terms of size effects, both adsorption and interaction (frozen adsorbed structures) energies become stronger with increasing cluster sizes due to the increase in the number of TM atoms in direct contact with the (ZrO2)13 nanocluster. The structural and electronic properties change for each TMn/(ZrO2)13 system, indicating that these properties could be tuned through variables like the TM species, cluster size and morphology (isomers with different structures). The results also indicate that, from the studied TMs, Ni (Cu) should form the smallest (largest) clusters when supported on the (ZrO2)13 nanoclusters. These and other results discussed here help understand the formation of the nano-interface in the TM-ZrO2 systems, which can be useful in the development of new catalysts.

The adsorption and growth of Agn (n = 1–4) clusters on cubic, monoclinic, and tetragonal ZrO2 surfaces: a first-principles study

The adsorption and growth of silver clusters on different zirconia surfaces.

Facile synthesis of ordered mesoporous Ni–Zr–Al catalysts with high hydrothermal stability for CO methanation

The ordered mesoporous Ni–Zr–Al catalyst exhibits high hydrothermal stability as well as high anti-coking and anti-sintering properties, due to the confinement effect of the mesopore channels and the incorporation of the ZrO₂ species.